A. Field of Invention
This invention pertains to a method and apparatus for encoding data at one of several data rates and more particularly to a method and apparatus which allows the data so encoded to be decoded at two or more rates. The scheme or method and apparatus is particularly useful in the transmission and storage of audio or video information.
B. Description of the Prior Art
Audio programs are often transmitted or recorded as digital data by converting the analog signals. In order to achieve high quality sound a sampling rate is used to sample the analog signal being transmitted or recorded and a high number of bits is used to represent each sample. For example, for CD recordings, or CD quality signal transmissions, sampling rates of up to 96 KHz and 192 KHz are used and each sample is converted to 20-24 bits. One disadvantage of this process is that, in some instances, a high quality sound may not be desired by the customer or his equipment may not be capable a replaying efficiently enough and a low sampling rate of 32 or 48 KHz and an A/D conversion rate of 8-16 bits/sample may be sufficient. Therefore, much of the data produced by the high quality conversion is unnecessary. Therefore it is desirable to have an encoding scheme which allows the transmittal or recording of signals at a very high quality, but which also allows these signals to be received or playback selectively either at the same high quality as they were transmitted or recorded, or at a lower quality.
A further disadvantage of existing encoding schemes is that they are highly inefficient and hence require a high band width to transmit or record unless complex compression algorithms are used.